<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>jQuery案例</title>
    <script type="text/javascript"src="../js/jquery-3.3.1.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            alert("HLOMASTER");
        })
    </script>
    <script type="text/javascript">
        $(document).ready(function () {
            //选择h3标签和class="content"元素的并集，将其背景设置为yellow
            $("h3,content").css("background","yellow")
        })
    </script>
</head>
<body>
      <h2 class="content">class为content的h2...</h2>
      <h3>h3...</h3>
      其他
</body>
</html>